Network storages that provide a file system to a host apparatus such as a business server are known. As the network storage, for example, there is a storage apparatus such as a network attached storage (NAS) that implements a file system such as a network file system (NFS) and provides it to a host apparatus.
In the network storage, there are cases in which data migration between file systems, for example, online migration (hereinafter, also referred to simply as “migration”) is performed. In the online migration, data of a migration source file system which is in operation is moved (transferred) to a migration target file system without stopping a user business.
Hereinafter, the migration source file system and the migration target file system are also referred to as a “source” and a “target,” respectively. Further, a source network storage and a target network storage are also referred to as a “source storage” and a “target storage,” respectively.
Patent Document 1: Japanese Laid-open Patent Publication No. 2015-179425
Patent Document 2: Japanese Laid-open Patent Publication No. 2010-262488
Patent Document 3: Japanese Laid-open Patent Publication No. 2014-10540
Patent Document 4: International Publication Pamphlet No. 2015/068208
In the network storage, there are cases in which availability and reliability of the system are decreased during execution of the migration.
For example, in the migration, when an access request such as an NFS request is issued to a storage area in which data is not moved yet, the target storage may process the NFS request after acquiring data from the source. At this time, there are cases in which, when it takes time to acquire data from the source, a business server determines it to be an input/output (I/O) timeout error with respect to the issued NFS request, and a business is unable to be continued.
In addition, there are cases in which the NFS request for files that have undergone the data movement (transfer) is executed in the target storage rather than the source storage. In the migration, since movement completed files are deleted from source and exist only in the target, when a storage failure occurs in the target during the migration, business data which is being operated may be lost.